High throughput electro-thermal poling

ABSTRACT

An apparatus for continuous electro-thermal poling of glass or glass ceramic material, includes a lower support conveying and contacting electrode structure, an upper contacting electrode structure positioned above the lower support structure, and one or more DC bias voltage sources connected to one or both of the upper contacting structure and the lower support structure. A process for continuous electro-thermal poling of glass or glass ceramic sheets or substrates includes heating the sheet or substrate, feeding the sheet or substrate continuously or continually, while applying a DC voltage bias, and cooling the sheet or substrate to within 0-30° C. of ambient temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 ofU.S. Provisional Application No. 62/969,011, filed Jan. 31, 2020, thecontent of which is incorporated herein by reference in its entirety.

BACKGROUND

This disclosure relates to electro-thermal poling of glass, andparticularly to processes and apparatuses for high-throughputelectro-thermal poling of glass.

The mechanism of thermal poling of glass or glass ceramic materials isthe result of ionic conduction, which is temperature dependent. A DCvoltage applied across a glass or glass ceramic which is at elevatedtemperature provides the driving force for mobile ionic charge migrationtoward opposing electrodes—i.e., cations migrate toward the cathode(s).The thermal poling process can be applied to glass and glass-ceramicmaterials which have a composition containing network-modifying ions. Apredominant effect of poling is the creation of an alkali-ion depletionlayer within the glass surface nearest the anode. The alkali iondepletion layer has a modified composition compared to the bulkcomposition, by which certain properties in the layer can be enhanced orobtained.

Potential enhanced properties include optical, chemical, physical andbioactive properties at the surface and/or near-surface layers. Glassproperties are altered by electrochemical effects that occur within aglass containing network modifying ions when exposed to an externallyapplied electrical potential. Glass properties vary considerablydepending on composition. Demonstrations of thermal poling have provedbeneficial on a variety of properties on a wide range of parent glasscompositions.

Prior art has demonstrated the advantages of thermal poling. However,all of these trials have been on a laboratory scale that is timeconsuming and has not been applied to bulk manufacturing amounts ofglass.

SUMMARY

Disclosed herein is an apparatus for continuous electro-thermal polingof glass or glass ceramic material, includes a lower support conveyingand contacting electrode structure, an upper contacting electrodestructure positioned above the lower support structure, and one or moreDC bias voltage sources connected to one or both of the upper contactingstructure and the lower support structure.

Also disclosed is a process for continuous electro-thermal poling ofglass or glass ceramic sheets or substrates includes heating the sheetor substrate, feeding the sheet or substrate continuously orcontinually, while applying a DC voltage bias, and cooling the sheet orsubstrate to within 0-30° C. of ambient temperature.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments as described herein, including the detailed descriptionwhich follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understanding the natureand character of the claims. The accompanying drawings are included toprovide a further understanding, and are incorporated in and constitutea part of this specification. The drawings illustrate one or moreembodiment(s), and together with the description serve to explainprinciples and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing aspects of a process according to anembodiment of the present disclosure;

FIG. 2 is a diagrammatic side view of a substrate or sheet and anapparatus for continuous poling of the substrate or sheet according toan embodiment of the present disclosure;

FIG. 3 is a diagrammatic side view of an apparatus for continuous polingaccording to another embodiment of the present disclosure;

FIG. 4 is a diagrammatic side view of one embodiment of a roller usefulin embodiments of the present disclosure;

FIG. 5 is a diagrammatic side view of an apparatus for continuous polingaccording to still another embodiment of the present disclosure;

FIG. 6 is a diagrammatic side view of an apparatus for continuous polingaccording to yet another embodiment of the present disclosure;

FIG. 7 is a graph of various types of change in applied voltage overtime useful in various embodiment of the present disclosure;

FIG. 8 is a diagrammatic side view of an apparatus for continuous polingaccording to yet another embodiment of the present disclosure;

FIG. 9 is a diagrammatic side view of an apparatus for continuous polingaccording to yet another embodiment of the present disclosure;

FIG. 10 is a diagrammatic side view of an apparatus for continuouspoling according to yet another embodiment of the present disclosure;and

FIGS. 11A and 11B are diagrammatic side views of an apparatuses forcontinuous poling according to two example embodiments of the presentdisclosure employing brushes.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiment(s).

As shown in FIG. 1 , a continuous thermal poling process 100 accordingto an embodiment of the present disclosure comprises the step 120 ofheating the glass or other sheet or substrate to a temperature Te withinthe range of from 100° C. to Tg (where Tg is the glass transitiontemperature; the step 130 of feeding the sheet or substrate continuouslyor continually while applying a DC voltage bias VB within the range offrom 100V to 10 kV; the step 140 of maintaining a constant VB, orramping or stepping up VB (and optionally, thereafter maintaining aconstant VB, and in any case applying the VB, whether constant or rampedor both, for a time Ti within the range of from 2 seconds to 30 minutes;and the step 150 of cooling the sheet or substrate to within 0-30° C. ofambient temperature.

Step 120 can optionally be conducted in continuous fashion. Steps 130and 140 can optionally be conducted in an inert or low-reactivityatmosphere. Step 130 can optionally include applying voltage by contactwith the substrate or sheet. Step 150 can optionally be performed duringthe time Ti of step 140. Step 150, particularly if not performed duringthe time Ti of step 140, is desirably performed within 2 seconds to 5minutes. The step 150 desirably includes cooling to within 0-10° C. ofambient temperature. The DC voltage bias applied in steps 130 and 140may additionally have an time varying voltage superimposed upon the DCvoltage bias.

The high throughput thermal poling process utilizing the steps describedabove with reference to FIG. 1 may be accomplished by utilizing any of avariety of equipment designs. Examples of equipment designs aredescribed below, but the embodiments shown are not to be understood asthe only possible implementations of the disclosed process.

With reference to FIG. 2 , the first example embodiment of an apparatus10 useful for practicing the process of the present disclosure comprisesof a series of aligned bottom rollers 30 and aligned top rollers 40,with each respective series of rollers connected electrically inparallel to a voltage source V, ensuring that the voltage applied to thesubstrate or sheet 20 is the same across each contact point between thesubstrate or sheet 20 and rollers 30, 40. As one example using DCvoltage, the top rollers 40 will have the positive bias while the bottomrollers 30 will have the negative bias to ground.

A preheated sheet or substrate 20 of glass or glass ceramic is passedbetween the rollers 30, 40 as shown in the figure. The glass will bethermally poled in a line contact area across the sheet between therollers of opposite voltage bias. The rollers will pull the sheet ofglass along the system to the next rollers for a cumulative residencetime during the thermal poling process at a continuous linear velocity.

The rollers can optionally have varying roller diameters and pitchesbetween rollers to increase or decrease the thermal poling residencetime that the sheet or substrate 20 experiences in contact with therollers, which function as electrodes in the poling process. Some othervariations of the electrodes and rollers are shown in additionalfigures. A simple variation of an apparatus 10 having smaller rollerdiameters is shown in FIG. 3 .

The rollers of any of the present embodiments can be compliant to thesubstrate or sheet by either structural or material methods, or by meansof compliant suspension of the rollers. Some examples of complaintrollers for use with glass are discussed, for instance, in U.S. Pat.Nos. 8,991,216B2 and 9,016,093B2. An example of a compliant roller 50,in this case produced by a 3D laser powder bed fusion printing process,is shown in diagrammatic side view in FIG. 4 . A hub or axle 52 supportsa rim 54 by multiple interleaved spiral spokes 56 which act during useas compliant springs.

With reference to FIG. 5 , according to other embodiments of theapparatus 10 of the present disclosure, the applied voltage may varyindependently at each roller, with voltage sources V₁ to V_(n)corresponding to n total rollers with an applied voltage. For instance,the applied voltage can be increased along the line of rollers, inducingmore current flow through the sheet or substrate and further enhancingthe effects of thermal poling as the sheet or substrate passes. Thenumber of steps taken in applied voltage can be configured by the numberof rollers in the system anywhere from a single roller and resultingsingle voltage step up to any number n of rollers, as shown in thefigure.

The voltage can also be applied by many other configurations, such aspairs of rollers (or more than pairs) that are tied to the same voltage.This concept is shown in the apparatus 10 of FIG. 6 , with the top setof rollers arranged in pairs 40 a, 40 b, still being the anode side andthe bottom rollers arranged in pairs 30 a, 30 b, being the cathode side,for example. Instead of all the rollers being electrically connected inparallel, the rollers are separated into pairs and connected to voltagesources V1-V4, of increasing voltage, left to right, as the sheet orsubstrate passes along the poling system apparatus 10.

Controlling the applied voltage of the rollers independently (or inpairs or larger groupings that a still smaller than the total) allowsfor voltage ramping as illustrated in FIG. 7 . Voltage ramping isdesirable to avoid dielectric breakdown in the substrate or sheet andallows the process to respond to the field produced in the substrate byion migration, allowing the substrate itself to respond with further ionmigration. As shown in the figure, the increasing applied voltage canincrease in either linear or nonlinear fashion. Linear steps produce afixed rate of voltage increase over the time that the glass makescontact with the rollers or poling system. A nonlinear increase involtage can decrease the required time for poling and optimize thepoling process in terms of manufacturing time. Therefore, a nonlinearramp can be desirable to reduce poling time while maximizing the depth(thickness) of the modified region of the substrate or sheet.

With reference to FIG. 8 , another variation of a high throughput polingsystem apparatus 10 consists of electrodes with flat upper surfaces,such as in the form of trays 60, which carry substrates or sheets 20,and which travel on a conveyor system and make contact with a voltagesource or sources as they pass. For example, trays 60 can make contactwith ground and become the cathode, replacing the bottom set of rollersshown in earlier embodiments. The single set of upper rollers 40 of thisembodiment would desirably still be the anode side that thermally polesthe sheets or substrates as they pass under. The cathode trays 60 willbe travel at the same linear velocity as the surfaces of the rollers 40.The number of rollers will be dependent on the effective poling time forthe formation of a desired ion depletion layer thickness.

The surface of the rollers can be either smooth or textured. Smoothrollers will make uniform contact with the glass and create a uniformdepletion layer thickness where electrical contact is made with theglass. Textured roller can be used to create differential thermal polingareas on the glass as well as creating surface structural features viaelectrical imprinting.

With reference to FIG. 9 , still another embodiment of an apparatus 10removes the rollers from the system and replaces them with respectivepneumatic arms or other mechanism(s) that lower respective flat-surfaced(flat bottom-surfaced) upper electrodes 70 to make contact with theglass sitting on trays or other conveyor structure. The example shown inFIG. 9 has the pressing arm as the anode and the trays or other conveyorstructure as the cathode. The respective anodes 70 travel on a rotatingturret or the like to match with the motion of the cathode conveyor ortrays to make constant contact with the substrate or sheet duringpoling. Once the desired thermal poling process has completed therespective anodes are raised and rotated back to the starting positionto repeat.

This embodiment is useful for when longer contact times are needed forthe desired poling process to occur. Again, the anode arm surface can beflat as mentioned to make uniform contact, or textured to makedifferential contact, if desired. The pressing anode and the cathodetray can also have 3D surface shapes to enable thermal poling ofsubstrates or sheets having curved surfaces.

With reference to FIG. 10 , according to another embodiment apparatus 10which is particularly useful if longer poling times are needed, conveyorbelts 80 could be set up with a poling voltage across them. Thesubstrate or sheet is then fed through as depicted in the figure. Thetop set of rollers and conveyor structure could be the anode, with thebottom set the cathode, or vice versa. Increase in voltage steps, ifdesired, can be accomplished by setting multiple such conveyors inseries provided with increasing voltages.

The apparatuses described herein can be used for feeding continuoussheets or single article substrates continuously into the process. Theelectrode fixtures can be held by electrically insulating materials suchas refractories to prevent heat loss and electrical shorts in the polingcircuit for safety.

With reference to FIGS. 11A and 11B, additional embodiments of anapparatus 10 can employ flexible contact electrodes, such as end-contactbrush electrodes 82 or side-contact brush electrodes 84.

The electrode materials used can be either ion-blocking or non-blocking.Ion-blocking electrodes prevent the migration of mobile ions from theglass into the electrodes/environment and vice versa. Non-blockingelectrodes allow for the migration of mobile ions across the electrodeglass interface and potentially with the environment.

Thermal poling methods and apparatuses of the present disclosure havethe ability to selectively alter glass composition and surfacetopography depending on electrode contact area which can be controlledor varied by patterning. The electrode could be patterned using machinetooling, additive manufacturing or lithography techniques. Thermalpoling has the ability to pole an article of glass at once instead ofrastering across it such as laser ablation or without masking forchemical etching. The main mechanism of thermal poling is ionicmigration which is driven by electric field lines and therefore cancreate higher resolution features than thermal pressing and most laserablation and chemical etching techniques.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the disclosure.

What is claimed is:
 1. An apparatus for continuous electro-thermalpoling of glass or glass ceramic material, the apparatus comprising: alower support conveyor and contacting electrode structure, wherein thelower support conveyor and contacting electrode structure comprises aplurality of moveable trays; an upper contacting electrode structurepositioned above the lower support conveyor and contacting electrodestructure; and one or more DC bias voltage sources connected to one orboth of the upper contacting electrode structure and the lower supportconveyor and contacting electrode structure.
 2. The apparatus accordingto claim 1 wherein the lower support conveyor and contacting electrodestructure comprises a lower conveyor belt.
 3. The apparatus according toclaim 1 wherein the upper contacting electrode structure comprises aplurality of upper rollers.
 4. The apparatus according to claim 1wherein the upper contacting electrode structure comprises a pluralityof upper flat contacting structures.
 5. The apparatus according to claim1 wherein the upper contacting electrode structure comprises an upperconveyor.
 6. The apparatus according to claim 1 wherein the uppercontacting electrode structure comprises a flexible contactingstructure.
 7. The apparatus according to claim 6 wherein the flexiblecontacting structure comprises a contacting brush.
 8. A process forcontinuous electro-thermal poling a sheet or substrate of glass or glassceramic material, the process comprising: heating the sheet or substrateto a temperature Te within the range of from 100° C. to Tg, where Tg isthe glass transition temperature of the material of the sheet orsubstrate; feeding the sheet or substrate continuously or continuallyusing an apparatus while applying a DC voltage bias VB within the rangeof from 100V to 10 kV; applying the VB, whether constant or ramped orboth, for a time Ti within the range of from 2 seconds to 30 minutes;and cooling the sheet or substrate to within 0-30° C. of ambienttemperature; wherein the apparatus comprises: a lower support conveyorand contacting electrode structure, wherein the lower support conveyorand contacting electrode structure comprises a plurality of moveabletrays; an upper contacting electrode structure positioned above thelower support conveyor and contacting electrode structure; and one ormore DC bias voltage sources connected to one or both of the uppercontacting electrode structure and the lower support conveyor andcontacting electrode structure.
 9. An apparatus for continuouselectro-thermal poling of glass or glass ceramic material, the apparatuscomprising: a lower support conveyor and contacting electrode structure;an upper contacting electrode structure positioned above the lowersupport conveyor and contacting electrode structure, wherein the uppercontacting electrode structure comprises a plurality of flat electrodesand a plurality of pressing arms, each of the plurality of flatelectrodes attached to one of the plurality of pressing arms; and one ormore DC bias voltage sources connected to one or both of the uppercontacting electrode structure and the lower support conveyor andcontacting electrode structure.